In a known switching device, a control or auxiliary current excites the magnet drive, which keeps the movable and the fixed contact pieces in contact with one another in a power circuit as long as the control current flows. Such a switching device is in particular also referred to as a contactor. However, it is likewise also possible to keep the circuit open as long as the control current flows. Then, the power circuit is closed when the magnet drive is switched off. Accordingly, a power circuit can be closed or opened by a weak control current.
If the control current is switched off, the contact carrier accelerates in the direction of the off stop as a result of the stored energies of the restoring device, in the configuration of a contactor the contact between the fixed and the movable contact pieces being opened. As a result of the acceleration, the contact carrier strikes the off stop at high speed.
The contact carrier striking the off stop results in considerable loading of the mechanism of the switching device. In the case of the several million switching cycles which can be achieved nowadays, this results in a high degree of wear not only on the parts directly involved and therefore in the possible life of the switching device being limited. Furthermore, the contact carrier striking the off stop as a result of the enormous acceleration occurring in the process also results in a negative acoustic influence on the surrounding environment.
Furthermore, the switch-off capacity of a switching device in the form of a contactor can be negatively influenced by high rebound values and an associated short-term reduction in the contact opening. This can only be counteracted by the switch-off speed being kept low, as a result of which, however, it is not possible to realize short switching times.
In order to solve the problem mentioned, damping materials on the off stop are known which damp the stop. Disadvantageously, such damping materials have a limited life. The enormous mechanical loading can also only be absorbed to an unsatisfactory extent. The noise loading can therefore also only be reduced within certain limits.
WO 01/41175 A1 has disclosed an electromagnetic switching device, which measures the distance/time response of a contact carrier with the aid of a magnetic field sensor and, as a function of the output signal of the magnetic field sensor, controls the current in the coil of the electromagnet system.
DE 100 10 756 A1 has disclosed a method for regulating the movement sequence of an armature, which method generates, by way of a control loop, a captive current for an electromagnet in order to achieve gentle striking of the armature.